Electrical cable having a self-sealing agent and method for preventing water from contacting the conductor

ABSTRACT

An electrical cable with a stranded central conductor encircled by insulation including a material which provides self-sealing properties to the cable present at least between the adjacent edges of the stranded conductor and the insulation. Preferably, the material is a polymeric material which is flowable at a temperature at least as low as 25° C. and has a 100 gram needle penetration value greater than 100 tenths of a millimeter at 25° C.

This application is a Divisional of U.S. Ser. No. 09/228,482, filed onJan. 11, 1999, which issued as U.S. Pat. No. 6,184,473 on Feb. 6, 2001.

BACKGROUND OF THE INVENTION

Insulated solid and stranded electrical cables are well known in theart. Generally stranded cables include a central stranded conductor witha protecting insulation jacket disposed around the conductor.

The most frequent cause of failure of directly buried aluminum secondarycables is a cut or puncture in the insulation inflicted during or afterinstallation. This leads to alternating current corrosion of thealuminum and finally to an open circuit. When a conductor is exposed towet soil, upon damage, leakage current may flow, and cause localizedelectrochemical conversion of aluminum to hydrated aluminum oxide andeventually to an open circuit of the conductor.

In the U.S., thousands of such instances occur annually and the repair(location, excavation, repair, and replacement) can be very costly. As aresult of the failures and in response to this problem, a tougherinsulation system was introduced and became an industry standard. Thetougher cable is described as “ruggedized,” and generally consists oftwo layers: an inner layer of high molecular weight polyethylene and anouter layer of high density polyethylene. This design is more resistantto mechanical damage than one pass crosslinked polyethylene, but stillcan result in exposure of the aluminum conductor if sufficient impact isinvolved.

Investigations show that AC electrolysis current can approach half-waverectification when the current density is high. This accounts for therapid loss of aluminum metal frequently experienced in the field. Acaustic solution (pH 10-12) develops at the aluminum surface anddissolves the protective oxide film.

The mechanism of aluminum cable failure is the formation of hydrousaluminum oxide. As the aluminum oxide solids build up, the insulation inthe vicinity of the puncture is forced to swell and splits open, makinglarger areas of the aluminum conductor surface available forelectrolysis, thus increasing the leakage current and accelerating thecorrosion process. Rapid loss of aluminum by AC electrolysis continuesuntil ultimately the cable is open-circuited. A caustic environment iscreated at the aluminum, electrolyte interface, which dissolves theprotective oxide film.

The ruggedized or abuse resistant type insulation was supposed toprotect the cable from physical abuse. While it helped this problem, itdid not eliminate 600 V cable failures. Utilities have recently reportedvarying numbers of 600 V aluminum underground distribution cable failurerates scattered between 70 and 7000 per year. Failures are evidenced byan open circuit condition accompanied by severe corrosion of thealuminum conductor.

All the reasons for 600 V failures are unknown, but several have beenpostulated by cable users. These cables seem to experience a high degreeof infant mortality, followed by failures occurring over decades. Theinfant mortalities are usually directly related to damage caused byadjacent utilities, damage inflicted by landscaping and planting, ordamage to the cable prior to or during installation. The failuresoccurring years later are harder to explain. There have beenpostulations of lightning damage, manufacturing defects, or insulationdegradation over the life of the installation.

In order to better understand the insulation characteristics, studies ofthe AC breakdown, and DC impulse breakdown were conducted. AC breakdownstudies on several different cables showed a high safety margin ofperformance. Each of these cables had a 0.080 inch wall thickness. Testswere conducted in water filled conduits. The AC breakdown strength ofall of these cables was consistently above 20 kV, far in excess of theoperating stress.

Impulse breakdown studies have also been performed on several 600 Vcable constructions having different insulation formulations. Theimpulse breakdown level of these cables was approximately 150 kV. Thisexceeds the BIL requirements of a 15 kV cable system and should wellexceed the impulses on 600 V secondary cables during operation.

The above margins of electrical performance were measured on new cables.They are far above what is needed to operate on a 600 V system sincemost of these cables operate at 120 V to ground. One of the tests duringcompound and product development is a long term insulation resistancetest performed in water at the rated operating temperature of theinsulation. For crosslinked polyethylene cables the water temperature is90° C. The insulation resistance must demonstrate stability and be aboveminimum values for a minimum of twelve weeks. If there is instabilityindicated, the test is continued indefinitely. Relative permittivity ismeasured at 80 v/mil and must meet specific values. Increase incapacitance and dissipation factor are also measured in 90° C. waterover a 14 day period. Insulation compounds used in present day cableseasily meet these requirements.

Manufacturing defects in cable insulation are found during production byeither of two methods. During the extrusion process, the cable is sentthrough a spark tester, where 28 kV DC, or 17 kV AC, is applied to theinsulation surface. Any manufacturing defect resulting in a hole in theinsulation will initiate a discharge, which is detected by the sparktester. Most manufacturers use this method. Another test that is alsooften employed is a full reel water immersion test. In this test 21 kVDC, or 7 kV AC is applied to the cable after immersion for 1 hour or 6hours, depending on whether the cable is a plexed assembly or singleconductor, respectively. The actual voltages used for these tests aredependent on the wall thickness. The above values are for an 0.080 inchwall.

The above testing has demonstrated electrical performance that is stableand far surpasses the requirements of the installation for 600 V cable.This does not explain a sudden cable failure after many years ofoperation. Such sudden failure can be explained by a betterunderstanding of the failure mechanism. Aluminum corrosion in thepresence of an alternating leakage current is a combination of twodifferent mechanisms. Aluminum is normally afforded a great deal ofcorrosion protection by a relatively thin barrier layer of aluminumoxide, and a more permeable bulk layer of oxide. However, flaws orcracks exist in these layers which provides a spot for the corrosionreaction to begin. The metal in contact with water undergoes an anodic(positive ions moving into solution) and a cathodic cycle, sixty timesper second.

During the anodic half cycle of leakage current, aluminum ions leave themetallic surface through these flaws and combine with hydroxyl ions inthe water surrounding the cable. This reaction results in pitting of themetal and the formation of aluminum hydroxide, the whitish powderevident in corroded cables. Another important reaction also occurs. Thehydroxyl ions are attracted to the metal surface during this half cycle,which increases the pH, causing a caustic deterioration of the oxidelayer, further exposing more aluminum.

During the cathodic half cycle another reaction occurs. Hydrogen ionsare driven to the aluminum surface. Instead of neutralizing the caustichydroxyl concentration, the hydrogen ions combine and form hydrogen gas,which leaves the cable. The hydrogen depletion has the effect of furtherconcentrating the caustic hydroxyl ions, thus furthering thedeterioration of the surface oxide. No pitting occurs during this halfcycle since the aluminum ion is attracted to the metal. A causticsolution develops, hydrogen evolves, aluminum pitting takes place, andaluminum hydroxide forms during this reaction.

A critical current density is necessary to sustain the corrosionreaction. Below this current density corrosion will be very slight, oralmost imperceptible. Once the current density is high enough, thereaction can be swift. The necessary current density is below 1 mA/in².The current density of a damaged 600 V cable is influenced by thevoltage, leakage resistance, and the area of exposed metal. Variablesaffecting this can include dampness of the soil, chemistry of the soil,degree of damage, etc.

The toughest cables on the market today will not always stand up to therigors of handling, installation, and operation. And exposed aluminumwill eventually deteriorate. The solution, then, is to find a way toeconomically prevent the corrosion process.

DESCRIPTION OF THE RELATED ART

Attempts have been made to prevent the ingress of moisture byintroducing a sealant between the strands of the conductor and betweenthe conductor and the insulation. See U.S. Pat. Nos. 3,943,271 and4,130,450. However, it has been found that the mere introduction of asealant into such spaces is not entirely satisfactory. Attempts toprevent moisture from reaching the conductor, such as using waterswellable material, have not met with technical and/or economic success.For example, voids may be formed in the sealant during the applicationthereof or may be formed if the cable is accidentally punctured. Anysuch spaces or voids form locations for the ingress of moisture whichcan lead to corrosion of the conductor and conventional sealants used inthe cables cannot eliminate such voids.

A prior art attempt to minimize the flow of moisture or water within theinterstitial spaces of a stranded conductor came in the form ofcompacted or compressed stranded conductors. The stranded conductoritself was radially crushed in order to reduce the diameter of theconductor and to fill the interstitial spacing with metal from theindividual wires themselves. The drawback to this method is that eventhough some deformation of the individual wires does take place, andsome of the interstitial spacing is filled, there is still thepossibility of cable insulation damage through which moisture can enterthe cable and contact the conductor.

Another attempt at correcting moisture flowing within interstitial spaceconsisted of filling the interstitial space with a foreign substancewhich physically prevented the flow of the moisture or water within theconductor structure. These substances typically comprised some type ofjelly base and a polyethylene filler material. At slightly elevatedtemperatures, this compound becomes fluid and viscous and can be appliedas the conductor is being formed. The individual wires used to form theconductor are fed into an extrusion die where the moisture blockingcompound is extruded onto and around each individual wire and, as thewires are stranded into the conductor, the interstitial space is filledwith the jelly-like material. Upon cooling, the filler becomes verystable and immobile and does not flow out of the interstitial spaces ofthe stranded conductor. Once the filling compound is applied within theinterstitial spaces of the stranded conductor, it tends to remain inplace. The problems encountered in applying such a filling substancerevolve around precise metering of the material into the interstitialspaces as the stranded conductor is being formed. If too much materialis extruded into the conductor, the outer insulation will not fitproperly. If too little material is applied, the interstitial spaceswill not be filled and therefore will allow moisture to flow within theconductor.

Another drawback to this method of applying a moisture blocking materialis that an extrusion head and an extrusion pump for applying thematerial is required for every individual layer of wires used to formthe conductor. The problems described above regarding the regulation ofthe volume of material applied through an extrusion head are multipliedevery time an additional extrusion pump and extrusion head is requiredwithin the conductor manufacturing system. Prior art efforts tomanufacture an acceptable moisture blocked conductor revolved aroundmethods for uniform application of the moisture blocking material to theconductor, but did not solve the problems created by handling andinstallation damage.

Applications of moisture blocking material to the spacing of concentriclay conductors is known within the industry. This can be found in U.S.Pat. Nos. 3,607,487; 3,889,455; 4,105,485; 4,129,466; 4,435,613;4,563,540; and 4,273,597.

U.S. Pat. No. 4,273,597 shows a method of strand filling theinterstitial spacing of a conductor with a powder. This is accomplishedby passing the strands through a fluidized powder bed, where theinterstitial spacing is filled with the powder. The stranded conductorthen exits the opposite end of the bed where an insulating layer isapplied which prevents the powder from vacating the interstitial spacingof the conductor.

U.S. Pat. No. 4,563,540 describes a conductor which is constructed byflooding a waterproofing material among the individual conductors whichmake up the core of the stranded conductor. This flooded core is thenwrapped with a plurality of different layers of shielding material whichprevents the influx of moisture into the stranded conductor.

U.S. Pat. No. 4,435,613 describes a conductor constructed of a pluralityof layers of insulating material with the core (or conducting portion)of the conductor being filled with an insulating layer of polyethylene.This polyethylene layer is contained by other rubber and plastic andepoxy compounds which produce a conductor having a waterproofconstruction.

U.S. Pat. No. 4,129,466 deals with a method for the application of thefilling medium which is applied to a stranded conductor. This methodcomprises a chamber into which are passed individual wires that will beused to form the stranded conductor. These wires have a filling mediumapplied to them in the chamber. After the application of this fillingmedium, the conductor is passed through a chilling chamber where thefilling medium is cooled and allowed to solidify within the interstitialspaces. This method requires that the chamber containing the fillingmedium and the stranded conductor be both heated and pressurized. Theheat applied to the chamber reduces the viscosity of the fillingmaterial, while the pressure assures introduction of the material intothe interstitial spaces of the stranded conductor.

U.S. Pat. No. 4,105,485 deals with the apparatus utilized in the '466method patent previously discussed.

U.S. Pat. No. 3,889,455 discloses a method and apparatus for filling theinterstitial spacing of the stranded conductor in a high temperatureflooding tank. The individual wires are fed into a tank containing thefilling material, the material having been heated to allow it to becomeless viscous. The individual wires are stranded and closed within theconfines of the flooding tank and the finished conductor is withdrawnfrom the opposite end of the flooding tank where it is passed through acooling means. The disadvantages experienced here involve the practiceof stranding the conductor beneath the surface of an elevatedtemperature moisture block pool. No access, either visual or mechanical,to the conductor manufacturing process is practical.

U.S. Pat. No. 3,607,487 describes a method whereby individual strands ofwire are fed into a flooding tank which is supplied with heated fillingmaterial by a pump and an injection means. The stranded conductor iswithdrawn through the opposite end of the flooding tank, wiped in awiping die, wrapped in a core wrapper and then passed through a binderwhere it is bound. The bound, wrapped core is then passed through acooler which sets the filling material. The above described process isrepeated through another flooding tank, another cooler, another bindingmachine, another flooding tank, another extruder, another coolingtrough, and is eventually withdrawn from the end of the manufacturingline as a product having a plurality of layers of moisture blockingcompound which protects the conductor core. The disadvantages herecomprise a complex manufacturing line whereby moisture blocking materialis applied at many different locations, each having to be meticulouslymonitored and controlled in order for a proper conductor construction tobe obtained.

It can be readily seen from the above referenced methods and apparatusesthat moisture blocked conductors are known and it can also be recognizedthat there are major problems concerning the elimination of moisturecontacting the conductor as a result of handling and installation of acable.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to improvements in insulated solid andstranded cables.

In one embodiment of the invention, during manufacture of theself-sealing cable, a material which provides the cable with puncture,crack, and void self-sealing properties is included between theconductor and the insulation. An additional water barrier material mayalso be included between the insulator and the conductor. Preferably,both materials are included in the cable. In this way, not only are thevoids filled by the material, but the material will flow into any void,puncture, or crack formed in the insulation, thus preventing migrationof moisture, with the added safety of the additional water barrier. Whenan additional water barrier, such as a polymer sheet or film, is used,the self-sealing material is applied over such barrier between thebarrier and the insulation, in which case the self-sealing material doesnot contact the conductor.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will be apparent from thefollowing detailed description of the preferred embodiments thereof inconjunction with the accompanying drawings in which:

FIG. 1 is a cut-away, perspective view of a cable of the inventionshowing a stranded conductor, the insulation, and the material whichprovides the self-sealing effect;

FIG. 2 is an end view of the embodiment of the cable shown in FIG. 1;and

FIG. 3 is an end view of the cable shown in FIG. 2 having a break in theinsulation with the break sealed by the material.

DETAILED DESCRIPTION IN THE INVENTION

Although the principles of the present invention are applicable todifferent types of electric cables, the invention will be described inconnection with a known cable structure, such as a 600 volt cable, whichnormally comprises, as a minimum:

(1) A central conductor of stranded wires of a good conductivity metalsuch as copper, aluminum, copper alloys or aluminum alloys; and

(2) A layer of insulation around the stranded conductors which has beenextruded thereover.

FIG. 1 shows a cable 11 comprising a conductor 12 of stranded wires ofcopper or aluminum or alloys thereof. A layer 10 of material whichprovides the self-sealing effect encircles the conductor 12 and fillsany spaces between conductor 12 and an insulation jacket 13 whichencircles material 10 and conductor 12. Insulation jacket 13 is of knownmaterial and is preferably an extruded polymeric material.

Preferred material 10 comprises a polymer which can be readily pumped attemperatures at least as low as 25° C. Preferably, the polymer will be alow molecular weight polymer such as low molecular weight isomer. Othermaterials, or combinations of materials, with or without such polymers,having such characteristics may also be useful in the present invention.A polymer which has been found to be particularly suitable ispolyisobutene.

The preferred polymer of the present invention has very little or nosignificant Shore A hardness. A test of determining whether or not thepolymer has acceptable properties is the Penetrometer Test incorporatedin ASTM D5 Penetration of Bituminous Materials. The 100 grams needlepenetration value at 25° C. should be greater than about 100 tenths of amillimeter.

The material used to provide the self-sealing effect to the electriccable of the present invention has the following properties:

(a) The material is substantially insoluble in water;

(b) The material is a dielectric, i.e., it is non-conductive and is nota semi-conductor;

(c) The material causes the cable to be self-sealing, i.e., it willflow, at ambient temperature, into insulation voids and/or cracks andprevent contact between the conductor and moisture which could causecable failure; and

(d) The material does not absorb moisture or swell upon contact withmoisture.

In the preferred embodiment of the present invention, the material usedto fill the space between the conductor and the insulation is a compoundof low molecular weight isomer or a low molecular weight copolymer of anisomer. Preferably, the material is polyisobutene. Advantageously thereis little or no air present in the cable between the conductor and theinsulation.

The material of the present invention may optionally contain fillermaterial, but is essentially free of any solvents or oils.

The cable 11 described in connection with FIG. 1 can be used withoutfurther layers encircling the insulation jacket 13.

Also, in other embodiments of the present invention described herein,the conductor and layers of insulation can be the same as thosedescribed in connection with FIG. 1.

The cable 14 illustrated in FIG. 2 is an end view of cable 11illustrated in FIG. 1.

FIG. 3 is an end view of cable 11 shown in FIG. 1 and illustrates theself-sealing effect of material 10 which flows into a break in theinsulation jacket 13, thereby preventing moisture from coming intocontact with conductor 12.

It is to be understood that in the embodiments described which includeadditional layers of protective material between the conductor and theinsulation jacket, including an additional waterbarrier of a polymersheet or film, it is not essential that the jacket tightly enclose thelayers there within or enter into the spaces between the wires andprotective materials, i.e., the interior size of the jacket can beessentially equal to the exterior size of the elongated elements so thatcompression of the elongated elements, and hence, indentation of thelayers there within including the insulation, is prevented.

The cable of the present invention is of particular advantage in thatnot only does the material fill the space between the conductor and theinsulation as the cable is manufactured, but after the cable is placedin service the material will flow into any cuts or punctures formed as aresult of damage during handling and installation of the cable or itsuse in service. The stresses placed on the conductor and the insulationduring handling and installation of the cable, such as bending,stretching, reeling and unreeling, striking with digging andinstallation equipment can form cuts or punctures in the insulation andbetween the insulation and the conductor. Such cuts or punctures canalso be formed after the cable has been placed in service as a result ofdamage from adjacent utilities, homer owners, or lightening strikes. Ascan be seen from the Example, the cable of the present invention canprovide acceptable service even after the insulation has been cut orpunctured, exposing the conductor.

EXAMPLE 1

Defects which exposed the conductor were made in the insulation layer oftwo 600 V cable samples. On one of the cable samples, a layer ofpolyisobutene polymer had been applied to the surface of the conductor.The other cable sample did not have the polyisobutene layer. Both cablesamples were placed inside separate 1 liter glass beakers containing tapwater. Each cable sample was energized at 110 V to ground with ACcurrent. The sample which did not have the polyisobutene layer exhibitedsevere corrosion overnight. The sample containing the polyisobutenelayer exhibited no corrosion after being energized and submerged for 4weeks in tap water in the glass beaker.

Although preferred embodiments of the present invention have beendescribed and illustrated, it will be apparent to those skilled in theart that various modifications may be made without departing from theprinciples of the invention.

EXAMPLE 2

The conductors from seven 600 V cable samples approximately 12 inches inlength were coated with the polyisobutylene. A defect was made in themiddle of each sample which exposed the conductor. Three untreatedcables (without polyisobutylene) were similarly damaged to expose theconductor. Each of the cable samples was then placed inside a laboratoryrectangular soil box, across and through the long sides of the box,which was then filled with soil. Each sample was energized at 110 V toground. The soil box was periodically watered to insure that theconditions leading to AC corrosion were present. Measurements of leakagecurrent were taken to monitor the effect of the polyisobutylene layer onpreventing corrosion. Periodically, the ability of each sample to carry20 amps AC current was tested. Over a period of 2 months, all of theuntreated cables showed increasing levels of current leakage, indicatingprogressive corrosion. The ability of the untreated samples to carrycurrent deteriorated rapidly during this period. At the end of twomonths, untreated sample #1 was unable to carry more than 0.5 amps ACcurrent. Untreated sample #2 could carry only 12.2 amps while untreatedcable #3 could carry no more than 9.6 amps. Current leakage from theuntreated samples increased steadily over the 2 month test span from alow of 0.32 mA up to a high of 353 mA. In contrast, none of the treatedsamples showed a current leakage greater than 47.6 mA. After the initialreading on this sample showing 47.6 mA, the polyisobutylene apparentlysealed the defect as indicated by a drop in the current leakage to 0.37mA at the end of the 2 month test period. The other treated samplesshowed similar results, however most never showed leakage current over0.5 mA. In addition, all of the treated samples continued to carry 20amps current at the end of the 2 month test period.

What is claimed is:
 1. An electrical cable consisting essentially of aconductor, a layer of insulation around said conductor and a materialflowable at about 25° C. between the conductor and the layer ofinsulation which provides self-sealing properties to the cable andwherein said material is a dielectric that does not substantially absorbmoisture or swell upon contact with moisture having capacity, uponcreation of a discontinuity in the layer of insulation of reestablishingcontinuity in the layer of insulation in a reversible manner.
 2. Theelectrical cable of claim 1 wherein said material has a 100 gram needlepenetration value greater than 100 tenths of a millimeter at 25° C. 3.The electrical cable of claim 2 wherein said material contains inertfiller material.
 4. The electrical cable of claim 2 wherein saidmaterial is substantially free of solvents and oils.
 5. The electricalcable of claim 2 wherein said material is a polymeric material.
 6. Theelectrical cable of claim 5 wherein said material is made from lowmolecular weight copolymers of an isomer.
 7. The electrical cable ofclaim 5 wherein said material is made from isobutene copolymers.
 8. Theelectrical cable of claim 5 wherein said material is an isomer.
 9. Theelectrical cable of claim 1 wherein the conductor is formed by aplurality of wires stranded together.
 10. An electrical cable as setforth in claim 1 having empty spaces formed during or after a cablemanufacturing process wherein the empty spaces are formed prior toinstallation of the cable, during the installation of the cable, andafter the cable is placed in service, within said layer insulation andbetween said layer insulation and the conductor, contain the materialwhich provides the cable with self-sealing properties.
 11. A method ofmaking an electrical cable which migrates the effects of voids,puncture, or cracks formed in an insulation layer prior to installationof the cable, during the installation of the cable, and after the cableis placed in service comprising the steps of: (a) forming a conductor,(b) applying a layer of material flowable at about 25° C. which providesself-sealing properties on the exterior of the conductor; and (c)forming an layer of insulation around the conductor wherein saidmaterial is a dielectric that does not substantially absorb moisture orswell upon contact with moisture, has capacity, wherein upon creation ofa discontinuity in the layer of insulation in the cable, the materialwill reestablish continuity in the layer of insulation of the cable in areversible manner.
 12. The method of claim 11 wherein the conductor isformed by a plurality of wires stranded together.
 13. The method ofclaim 11 wherein said material has a 100 gram needle penetration valuegreater than 100 tenths of a millimeter at 25° C.
 14. The method ofclaim 13 wherein said material is a polymeric material.
 15. The methodof claim 14 wherein said material is an isomer.
 16. The method of claim11 wherein said material flows into voids, punctures, or cracks in thelayer of insulation formed during the installation of the cable.
 17. Themethod of claim 11 wherein said material flows into space between theconductor and the layer of insulation formed during the installation ofthe cable.
 18. The method of claim 11 wherein said material flows intospace between the conductor and the layer of insulation formed prior tothe installation of the cable.
 19. The method of claim 11 wherein saidmaterial flows into voids, punctures, or cracks in the layer ofinsulation formed prior to installation of the cable.
 20. The method ofclaim 11 wherein said material flows into voids, punctures, or cracks inthe layer of insulation formed after the cable is placed in service. 21.The method of claim 11 wherein said material flows into space betweenthe conductor and the layer of insulation formed after the cable isplaced in service.
 22. The method of claim 11 including applying a waterbarrier material over the conductor before applying the self-sealingmaterial in step (b).
 23. The method of claim 22 wherein the waterbarrier is a polymer sheet.
 24. A method for imparting to a cablecomprising a conductor and at least one insulating layer having acapacity of self-repairing the at least one insulating layer, the methodcomprising providing the cable with an inner layer comprising adielectric material that does not substantially absorb moisture or swellupon contact with moisture is flowable at about 25° C. and has thecapacity, upon creation of a discontinuity in the at least oneinsulating layer, of reestablishing the continuity in the at least oneinsulating layer in a reversible manner.
 25. The method according toclaim 24 wherein the material is capable of at least partially filingthe discontinuity without leaking from the cable in an uncontrolledmanner.
 26. A method for manufacturing a cable having a layer ofself-repairing material, comprising the steps of: (a) depositing theself-repairing material, maintained in a fluid state, on a cable core;and (b) forming the layer of self-repairing material so as to obtain auniform layer of predetermined thickness wherein said material is adielectric that does not substantially absorb moisture or swell uponcontact with moisture, is flowable at about 25° C. and has capacity,wherein upon creation of a discontinuity in a layer of an insulation inthe cable, the material will reestablish continuity in the layer ofinsulation of the cable in a reversible manner.